Blood pattern analysis

Blood Pattern Analysis (BPA) often provides crucial evidence from scenes of violent crime. When an incident occurs which causes bloodshed, blood may be deposited on nearby surfaces and on individuals. An examination and analysis of the blood pattern of any such deposited blood, by a forensic biologist, may give an indication of the mechanism of deposition and by inference an indication of the activity which caused the deposition.

Forensic biologists

Bloodstaining on items or individuals can be deposited in two ways, namely contact between surfaces and airborne deposition.

Contact bloodstaining arises as a result of two surfaces coming into contact with one another while one of the surfaces bears wet blood. Some contact stains can show details of the object that made the mark such as the pattern of fabric or hair. Smeared contact stains arise as a result of a moving contact between two objects, one of which is wet with blood.

Airborne bloodstaining arises as a result of wet blood becoming airborne, due to the application of force. The direction of travel of the blood can often be determined by conducting blood pattern analysis and the examination of the shape of the bloodstain.

Examples of airborne bloodstaining include:

Impact splatter , which is often seen in cases involving assault.

Passive drips, which come from blood falling under gravity from a source of wet blood i.e. the wound of a victim.

Cast off, which is typically found in cases involving multiple stab wounds to a small area of the torso or blows from a blunt object to the head of a victim.

Expirated blood, which results in blood in an airway of a victim (such as the mouth or nose) being expelled by the passage of air.

Blood transfer may be primary or secondary. Primary transfer occurs when an object wet with blood comes into direct contact with another surface. Secondary transfer occurs when an object wet with blood comes into contact with another object which then comes into contact with a third object , transferring wet blood in each case. When an assailant becomes blood stained, as a result of striking someone, blood is transferred directly from the complainant to the assailant i.e. there is primary transfer. If the assailant then touches a door handle with their now blood stained hands that represents secondary transfer.

Blood pattern analysis - case example

An altercation between a group of youths and a single male occurs in the street. This results in the male being stabbed and fatally wounded. The victim’s blood is deposited on the clothing of all of the youths and they are all subsequently charged with murder. The murder weapon (a knife) is later recovered but no DNA apart from that of the victim is recovered from it.

How can our forensic biologist assist the defence counsel?

Our forensic biologists have years of experience in blood pattern analysis (BPA) having given blood pattern analysis evidence and appeared as expert witnesses in many serious and high profile cases.

Our forensic biologist can:

Re-examine the blood pattern evidence previously examined by the prosecution as well as conducting new analysis on other items which may not have been initially submitted but which may be of significant evidential value even by their omission.

Re-interpret the evidence to see whether the blood deposited on their clothing is consistent with them being the knife wielder, somebody who also assaulted the victim or just a bystander to the assault and subsequent murder.

Examine the prosecutions interpretations and submit new interpretations of the blood patterns in question.

Provide a detailed forensic expert witness report commenting on all issues raised by the defence counsel together with expert opinion on any other aspects found to be relevant to the defendants case during our investigation.